Shaheen poses a significant challenge for the GOP, despite the party’s view that she is vulnerable.

A former governor who defeated Republican Sen. John Sununu in 2008, Shaheen already has nearly $3 million cash on hand for her reelection campaign. A Public Policy Polling survey in September found her with a 51 percent approval rating.

The two current Republican contenders, former state Sen. Jim Rubens and conservative activist Karen Testerman, aren’t considered top-tier candidates.

And two top Republican prospects for the race — state Senate Majority Leader Jeb Bradley and former Rep. Charlie Bass — have decided against running.

Brown could be the GOP’s last best hope. He’d enter the Republican primary with strong name recognition and easy access to cash. The PPP survey found Brown trailing Shaheen by 4 percentage points in a hypothetical race.

One national Democrat said the party “would take Scott Brown seriously.”

One New Hampshire Republican operative said Brown has built strong relationships with party activists with his repeated visits.

“Being receptive and responsive is kind of the New Hampshire way, and I think people like him doing that up here,” the operative said.

But with less than a year until Election Day, impatience is growing.

The conservative New Hampshire Union-Leader last month urged Brown to “stop flirting with” the state.

“Despite the curious way he’s going about this, most people — including me — continue to be pretty interested in Scott Brown,” Cullen said.

“It is time, though, if he were serious about it, to kind of get serious about it and start running.”